Two of the three men then held her while the third hit her in the face, leaving her with a black eye, she told the station. The men then fled.
She said more than a dozen people witnessed the incident, but no-one intervened.
On Wednesday, junior interior minister Marlene Schiappa – who is in charge of citizenship and was previously in charge of equality issues – visited the eastern city to discuss the safety of women in public.
She told France Bleu Alsace that “the skirt is not responsible for the attack and the woman even less”.
“A woman is never hit because she wears a skirt. A woman is hit because there are people who are misogynistic, sexist, violent, and who free themselves from any law and any rule of civility by striking them.
“When you’re a student and you have to think about the outfit you have to wear and the message it sends, it’s an overwhelming mental load,” Ms Schiappa said.
She also urged people to call the police if they witnessed any kind of street harassment incidents against women in a public space.